Poole — On the Distrihution of Aetivitij in Radmm Therapy. 477 



that the activity at the base of a sheet 1 mm. thick would be less than 1'12. 

 It would appear that the more porous the material used between the metal 

 and the skin the less should be the burning effect upon the latter. 



In the case of treatment with several parallel needles, each containing a 

 tube 15 mm. long, the distribution of activity in a perpendicular plane 

 through their centres can be found by summing the effects of the separate 

 needles for any required point. Where the area of irradiation is increased 

 by the use of long needles, which are partially withdrawn at intervals, so as 

 to move the emanation tube to a new position on the axis, the effect is similar 

 to that of a long emanation tube, and could be calculated by the same 

 method as that used above for the short tube. 



